Method of and circuit for material modification and coolant clarification



Dec. 11, 1951 R. B. BOOTH ET AL 2,578,040

METHOD OF AND CIRCUIT FOR MATERIAL MODIFICATION AND COOLANT CLARIFICATION Filed Sept. 3, 1942 2 SHEETS-SHEET l f- P To 5F Moo/F750 M4 Trp/,4 L To .5f Mop/fafa CONTM/HTFD COOLH/VT INVENTORS Raaf/Pre. 00 7H, Na/1MM Afa/MSH,

@ily/Www@ TTORNEY Dec. l1, 1951 R B, BOOTH p -rAL 2,578,040

METHOD OF AND CIRCUIT FOR MATERIAL MODIFICATION .AND COOLANT CLRIFICATION I Filed Sept. 5, 1942 2 SHEETS-SHEET 2 I llli fwn TEP kW@ TFA snm/6470A co/vrnM//VAM/rs f FPO TH INVENTORS Raaf-fri. goor/4 Noe/wmv www5/fA ATTORNEY Patented Dec. 11, 1951 S PATENT OFFICE METHOD F AND CIRCUIT FOR MATERIAL MODIFICATION AND COOLANT CLARIFI- CATION Robert Ben Booth, Springdale, and Norman Morash, Stamford, Conn., assignors to Ameri can Cyanamid Company, New York, N. Y., a

corporation of Maine Application September 3, 1942, Serial No. 457,190

i Claims.

' This invention relates to an apparatus for and method of' mechanically modifying materials where a lubricating cooant may be used to aid the modifying operations. More particularly, the invention relates to an apparatus for and method of removing foreign matter from The lubricating coolants used in conjunction with the material modifying operation. This application comprises a continuation-impart of our copending application, Serial No. 443,816 filed May 20, 1942.

Modern industrial practice involves a great many operations in which various objects are subjecied to mechanical treatment, usually to alter their size or shape. Illustrative of such procedures are the familiar operations of brushing, bufling, cutting, drilling, drawing, extruding, grinding, milling, rolling, sawing, tapping, threading and the like. These operations may modify only the external surfaces as in grinding or milling a piece to a specified dimension or in screwthreading stock. In other cases, a porlion of the material may be removed without appreciably a1- tering the external surfaces as in drilling, reaming and tapping operations. In still others, the entire shape of the object may be altered as when a blank is shaped by drawing, exiruding, rolling and the like operations.

Whatever the purpose or nature of these operations and whatever the nature of the material being worked upon, Whether metals, alloys, artificial plastics, glass, rubber, mica, porcelain, brous products or like materials which may be adaped to modification under such treatment, there is one feature which is common to all. That is the heating of both the material being treated and the operating tool as a result of the friction involved.

This generation of heat is unfortunate since it introduces certain difficulties into the carrying out of the material modifying operations. Among these are for example: the more rapid dulling and wearing of operating tools; difficulties in producing an exact size because of expansion under the infiuence of heat; spoilage and breakage of workpieces due io unequal expansion under the influence of heat; excessive power consumption; excessive corrosion and the necessity for working at speeds and pressures low enough to prevent excessive heating.

'In addition, there is in almost every case an accumulation of what, for the purposes of the present specification, may be called wase products. These waste products may comprise particles, chips or turnings of the material itself, as in cutting or grinding operations, or particles of the operating tool as in the case of grinding. Again, 'they may comprise corrosion or oxidation products such as rust in the machining of iron or steel; scale, as in the rolling or drawing of metals or oxide ms such as occur in drawing or extruding copper, brass, iron or aluminum and the like. Solid wastes, such as chips, turnings, dust, grit and the like, must be removed from around the workpiece and operating tool in order to facili ate working. Also, any corrosion and oxidation products usually must be either prevented from forming or be subsequently removed in order to obtain a final, finished article.

Largely because of these heating and waste accumulation features, it has become common practice in the material-working arts to make use of lubricating` and/or cooling fluids to facilitate the working operations, The use of these lubricating coolants is intended to perform one or more of several functions such as to provide lubrication between the operaing tool and the workpiece; dissipate heat and so cool the tool and workpiece; reduce the power consumed in carrying out the operation; increase the usable life of the tool; secure a good finish and accurate sizing; prevent corrosion or oxidation and ush or carry away cuttings, chips, grit, dust and the like. In some cases the cooling function is the more important and in others lubrication is the first consideration. The choice and nature of the fluid will depend, therefore, on the kind of work to be done more than on any oLher consideration. In almost every case, however, the fluid used performs both cooling and lubricating functions and therefore in the present specification and claims the expressions lubricating coolant and coolant" are used to designate these lubricating and cooling fluids generally.

The nature and constitution of these lubricating coolants may be almost as varied as are the operations in connection with which they may be used. They may comprise simple liquids, Water being commonly used, for example, in such operations as the grinding or cutting of rubber and artificial plastics; and kerosene, fuel oil, turpentine and the like in working upon glass and ceramics. Waier is also commonly used in connection with drawing, extruding and rolling operations, particularly on metals. In other cases an alkaline solution such as sal soda in water and/or soap solutions are often used. For still different purposes the use of oil such as mineral oils and fatty oils of the lard or whale oil types, tallow or mixtures of mineral and fatty oils have proved to be of advantage.

Still another type of coolant which is commonly encountered is the so-called soluble oil emulsion. Since these emulsions are most frequently used in cutting, grinding and drawing operations on metals and alloys, for which purposes they were originally prepared, they are also commonly referred to as cutting-oil" emulsions. These emulsions usually comprise light-oil solutions of various saponifled crude fats, various soaps such as mahogany soap, fatty acid soaps, naphthenic acid soaps, various lubricants, petroleum sulfonates and sulfates, sulfonated oils, etc., wetting agents, anti-oxidants, thinners, etc., which have been cut with water and emulsifled.

In any case, however, the lubricating coolant soon picks up and becomes contaminated with a considerable quantity of the waste products. Since these waste product contaminants often have an intrinsic value as, for example, in the case of metal cuttings of copper, bronze, aluminum, magnesium and the like, it is often desirable to recover them from the coolant. A still more important reason for removing the contaminants is that their presence always interferes with the eficient performance of the coolants intended function. This interference may occur either because the presence of foreign matter in the coolant reduces its cooling and lubricating capacity or because the foreign matter causes scratching and marring of the surface being worked upon.

Another troublesome type of interference with the coolants performance occurs in connection with the use of oils and emulsions. It is brought about by the heat of friction which causes a breakdown into sludge of the oils themselves or the oils, soaps or other constituents found in emulsion-type coolants. This sludge has a direct effect on the proper performance of the coolant since it not only changes the cooling power of the emulsion but also sharply reduces its lubricating value.

Where the coolant comprises a fluid such as water the recovery of the foreign matter for its which the cooling bath acquires a considerable content of metal oxides, salts and metal particles. Similar instances in which it may be desirable to recover material occur in connection with rolling operations and with many well known washing, pickling or descaling treatments. On the other hand, in many localities it is highly desirable or even necessary to clarify the water which has been used as a coolant for reuse. This is particularly true where large volumes of Water are used.

Where a compounded lubricating coolant is used. the coolant itself has a definite real value so that its reuse is important in carrying out an economical operation. This is particularly true, for example, in the cases where oils are used as flushing, dipping, cooling or washing baths and where the soluble-oil-type emulsions are used in cutting, drilling, grinding, milling and the like operations on metals. However, the presence of the contaminants definitely limits the reuse of the coolants.

There exists, therefore, a definite demand for a method and apparatus whereby the coolants may be clarified either to permit their reuse or to recover the valuable contaminants, as witnessed by the fact that many operators, in spitel oi' much eiort and experimentation on clarification methods, still discard their entire coolant baths after short periods of operation. Periodic rejection every eight hours or less is by no means uncommon particularly in precision work.

In the past there has been no satisfactory. eilicient and economical apparatus for or method of carrying out the material-modifying operations and also treating these lubricating coolants to remove the waste products and impurities therefrom. Settling tanks have been used. Many standard grinding and machining devices have such tanks built in as an integral feature. In other cases, central settling systems have been tried. However, neither individual nor central settling systems have proved satisfactory, principally because the large amounts of contamin,

ants which must be removed require either impractically large settling capacity or frequent stoppage of the material-modifying operations in order to clean out the settling vats. In both systems large amounts of coolant are wasted in the cleaning out process.

Centrifugal separation has also lbeen tried but has not proved wholly satisfactory for several reasons. The most troublesome of these include the relatively extensive equipment required to handle large volumes of fluid, the difficulty of applying this clarification method to individual material-modifying machines and the periodic dismantling of the equipment which is required for cleaning the centrifuge. Filtration also has proved impractical, both because of the equipment required, the frequent periodic clean-out necessary and the fact that many of the materials used as cooling uids or occurring therein as impurities, particularly extremely ne particles. were not susceptible to successful ltration. Certain filter media such as hair, ber, etc., may be temporarily cleaned by backwashing but eventually become sufficiently clogged to demand replacement.

It is, therefore, an object of the present invention to provide both an apparatus for and a method adapted to carry out the material-modifying operations and at the same time remove waste products from the lubricating coolants in an efficient but simple manner. In general this is accomplished by setting up a closed circuit including a material-modifying apparatus, a coolant supply and a clarifier or flotation cell, an excellent cell for the purpose being the well known Fagergren-type of U. S. Patents 1,963,122 and 2,101,331.

The invention will be illustrated in conjunction with the accompanying drawings in which:

Figure 1 is an elevation, partly in section, of one type of clarifier adapted for use in the material-modifying circuits of the present invention; and Figures 2 to 6 constitute diagrammatic representations of a number of material-modifying circuits embodying the present invention.

In the drawings, the illustrative clarifier of Figure 1 comprises an outer casing I enclosing three compartments 2, 3 and 4 which are separated from each other by means of partitions 5 and 6 and a false bottom 1. Chambers 2 and 3 are interconnected by a large opening 9 in the false bottom 1. Supported by the false bottom and immediately above opening 9 is located stator I0 of a mechanical-type flotation unit. Rotor Il, located within the stator, is turned by the rotation of shaft I2 which in turn may be motivated by any conventional driving mechanism. Mounted on the stator I0 and surrounding shaft I2 is a shield or hood. Il, resembling an inverted funnel. n n n Contaminated coolant. enters .the clarifier through inlet 8, passes through chamber 2 and into chamber 3 through opening 9 under the stator IIl. Rotation of rotor II not only agitates the coolant but draws air down through thean- 'nular space I3 between shaft I2 and hood I4,

forcing it into the liquid as fine bubbles. Under this combined agitation and aerating action, a froth layer containing substantially all the contaminants gathers at the surface of the coolant. Rotation of skimmer I5 by any conventional driving mechanism crowds the froth over tailgate I6 into launder Il by means of which it is conducted to any desiredl point. Clarified coolant flows over partition 6 into chamber 4, from which it is withdrawn and conducted to any desired point by conduit I8.

Three elements, the material-modifying device, the coolant supply and the flotation cell or clarifier, comprise the essential elements of the circuit of the present invention. Their exact arrangement in relation to each other may vary in accordance with the needs of the problem. For

example, the coolants may be stored in a tank andthe workpiece, after the modifying operation, may be passed into and/or through the coolant. This occurs, for example, in operations such as wire-drawing or where pickling and cools and lubricates but is also intended to flush the waste products from the point of operation. It is also useful where cooling is of primary importance and the fluid is sprayed or poured on dies, rolls, bearings and the like. A diagrammatic flow scheme in which the coolant supply is directly circulated is shown for example in Figure 2.

It may be desirable to use an additional supply or storage tank. In these instances the coolant is collected and fed to the flotation cell, clarified and the clarified coolant returned to the supply tank. Coolant from this tank may be sent to the material modifier as desired. One such arrangement is shown in Figure 3. Figure 3 also illustrates one method of treating the contaminant-bearing froth. It is sent to a settling tank and the solid matter allowed to settle after which it is removed as a sludge and the supernatant coolant returned to the inlet of the clarifier.

Use of a flotation cell in this way for the removal of the waste products from the lubricating coolant has been found to satisfy the requirements of the problem which the apparatus and process of the present invention was intended to solve. In our previously-mentioned copending application we have shown that a flotation machine may be satisfactorily employed to remove and recover waste products produced in metal-working operations from an emulsion-type lubricating coolant. According to the present invention, the teachings of our copending application may be extended to include not only emulsion-type-coolants but also those of simple fluid types, such as water or solutions of alkaline materials in water, and to oils either used alone or in mixtures with other oils. According to the present invention froth flotation may be used not only to separate metallicparticles from the coolant but also to separate and recover non-metallic materials such as rubber, glass, artificial plastics, ceramics and the like.

Both the apparatus circuit and the process of the present invention are highly flexible, thus giving the present invention an important advantage in that the material-modifying means to be incorporated into the operating circuit may be of substantially any type. For example, it may be of a type, the basic function of which is to carry out a cutting operation, such as a lathe, mill, drill or the like. Again it may be intended to perform a grinding function. Or the function may be to deform the workpiece into a wholly different shape such as the dies and rolls used in extruding, drawing and rolling operations.

It is also an important feature of the present invention that it is not limited in use to a flotation cell which operates on any fixed principle. It may be a strictly mechanical type in which air is introduced by agitation, or a cascade type in which air is introduced by tumbling the pulp. Good results may be obtained when subaeration cells are used, in which the air is introduced into the pulp either by a suction created by the moving parts of the machine or is released below the liquid surface under pressure. In still other cases, gas-generating materials may be added t0 the coolant and the liberated gas used to float the contaminants. If desirable this procedure may be supplemented by the aid of mechanical agitation or the application of a vacuum. In some cases, as in connection with grinding 0perations, the coolant is well aerated and the use of a simple Vacuum cell is wholly adequate. Standard equipment of many types is readily available. Most of the development work was done with a Fagergren flotation machine and excellent results were obtained.

In addition to the fact that the method and apparatus of the present invention is not limited to a flotation cell of any particular type, it also provides an extremely flexible arrangement suitable for use in different fields. Various types of flotation machines are commercially available with widely varying capacities. It is, therefore, both practicable and feasible to make use of a froth flotation circuit for each material-modifying machine which will have a capacity suitable thereto. Thus, for example, where an industrial plant has a number of machines operating on different types of materials, the cuttings or scrap from which has an intrinsic value, each material-modifying machine may have its own accompanying flotation machine. In this way scrap from the different types of materials may be recovered separately whenever it is desirable to do so.

On the other hand, large numbers of machines may be performing different types of operations on the saine material. In such a case all the scrap from the same material may be recovered by means of a centralized system even though the closed circuit with the flotation machine may include a plurality of material-modifying machines of the same or different types. It will also be apparent that where mixed types of material in the scrap are either unobjectionable or unavoidable, a centralized system may include not only 7 different types of machines but they may, be working on assorted materials. ,i

It is also an advantage that the process and apparatus may be efhciently used whetherv the operation is batch or continuous. Therefore, a single flotation machine may be introduced into a closed circuit with one or more material-modifying machines for a period of time sufficient to clarify the coolant being used in those machines and then disconnected and moved into conjunction and operation with other machines. A flow scheme suitable for such operations is shown for example in Figure 4 of the accompanying drawings. Similarly the method and apparatus circuit is not limited to the use of a single flotation machine but a plurality of machines may be operated either in parallel or in a string or series.

In froth flotation procedures as carried out in ore-dressing operations it is customary to make use of various frothers, promoters and modifying agents either to increase the amount of solids which can be iioated or to increase the selectivity so that only certain desired portions are caused to float. Ordinarily such problems are not encountered in clarifying coolants since here the peculiar problem of removing substantially all the solids is involved. Both because the composition of the coolant itself may vary and because the nature of the impurities depends upon the use to which the coolant has been put, the flotation problems may present widely varied aspects.

Coolants of the emulsion type usually present the simplest problems. Many of these are made from oil containing various soaps. It is often found that samples of contaminated emulsion froth readily when subjected to the action of a flotation machine and a good concentration can be had without the use of any additional reagents. When the oil component of the coolant shows such frothing and collecting power for the contaminants, it is frequently possible to take full advantage of this fact by introducing small amounts of the oil during the flotation operation. Thus these additions serve a dual purpose, that of promoting flotation and aiding the clarifying operation while simultaneously replenishing the oil content of the coolant. Such replenishment is periodically required because of spillage, removal on workpieces, etc. The flotation machine is an efficient means of dispersing the new oil in the coolant.

With other types of coolants, however, flotation without the use of reagents may not be effective in removing certain types of valuable contaminants. With materials of this kind it becomes necessary to make use of some froth flotation reagent or combination of reagents to insure a satisfactory result. This is usually true in those cases Where Water or aqueous solutions are used as coolants. Water itself has no noticeable collecting power and the usual components of aqueous solution coolants seldom include any material adapted to form a suitablek froth. Reagents of one type or another are almost certain to be required.

Coolants of the water-immiscible oil types, present an additional problem. These oils usually froth when subjected to the action of a flotation machine. However, the froth has little or no collecting power. Merely adding a otation reagent of the ordinary type does not normally solve the problem since the successful concentration by froth fiotation, using familiar types of reagents, appears to be dependent upon a surface effect which is either inhibited by the oil or is not exhibited by the oil. According to the present invention, it has been found that since these oils are ordinarily insoluble in and immiscible with water they may be mixed with water and temporarily emulsiied by the action of the notation machine although the emulsions readily separate into layers on subsequent standing. A diagrammatic flow scheme embodying these features is shown for example in Figure 5 of the drawings. Emulsion breakers may be used to speed up this separating process, if so desired. The contaminants are often found to be readily concentrated by the frothing which occurs during the temporary emulsifcation without the use of additional flotation reagents. Where the contaminants are not of a type adapted to be collected by this action alone, flotation reagents may be added and will produce effective concentration.

It is therefore apparent that the choice of reagent will depend both upon the results desired and upon the nature of the coolant being treated. In addition, care must be taken that the reagents selected will not. either by their inherent properties or because of the quantity required, modify the properties of the coolant and so interfere with its effective performance of its intended function.

The addition of one of the common frothers such as pine oil, cresylic acids. mixtures of the higher aliphatic alcohols and the like may prove adequate in removing the particular impurities in question. Again, it may be desirable to supplement their action by the use of various oils. These oils may be either of a saponiable type, such as the heavy glycerides, for example, or may be non-saponiable oils such as fuel oil, kerosene and various other hydrocarbons. These may act as collecting agents, frothing agents. froth modifiers or the like and may be used in a manner similar to that in which they are employed in the field of ore-dressing.

With many of the contaminated coolants found in actual practice, it is necessary to use a flotation reagent of the anionic-type for effective clarification. These may include, for example, such varied substances as fatty acids, resin acids. talloel and the like; soaps such as the alkali, amine and other soaps of the heavy organic acids, black liquor soaps, xanthates and di-thiophosphates. Whether the anionic reagent is used alone or in combination with other agents will again depend upon the nature of the contaminants and on the nature of the coolant.

On the other hand certain coolants may require the use of cationic-type reagents for efficient flotation treatment. Such reagents may include amines or polyamines; either as bases or as soluble salts such as the hydrochlorides, acetates, and the like; quaternary nitrogen compounds; pyridinium compounds; various cationic compounds formed by condensing polyamines such as ethylene diamine, diethylene triamine, hydroxyethyl ethylene diamine and the like with fatty acids, fatty acid glycerdes and the like.

In addition to the above described reagents, other classes of reagents known as modiflers" may be used. For example, in the flotation of metallic iron from certain coolants the use of heavy metal salts such as copper sulfate in combination with a promoter may be an advantage in securing more rapid or more complete removal of contaminants. Various other materials may be used with the contaminants in order to render them more floatable.

' As was pointed out, the grinding or cutting tool often develops a localized high temperature at the point of contact with the workpiece with a resultant breakdown of certain constituents of the coolant, such as fatty acids, into a sludge. This is doubly troublesome` in that the sludge formed by the breakdown not only destroys the efficiency of the coolant for lubricating and cooling purposes but after the clarification of the coolant these constituents are no longer present to perform their intended function. Because of this, where a fatty acid or fatty acid product flotation reagent can be used, they have the added advantageof replacing all or a part of the coolant composition lost by breakdown.

It is also an advantage of the present invention that, since only a small amount of reagent is normally required, it may often be added to or compounded with the coolant before use without any noticeable effect on the efficiency of the latter. Where the additional reagents are added at the time of flotation it is well, although not absolutely necessary, to condition the coolants with the reagents for a few seconds before starting the actual flotation. Or, if so desired, the reagents may be added either as a single amount or in stages during the actual flotation operation.

Where there is a central cutting and cooling oil circulating system in a machine shop the same coolant may eventually be used on a number of different materials. As a result, the impurities picked up by the coolant in the system may comprise quite a wide variety of different materials. It is often desirable not only to separate these constituents from the cutting oil but from each other and from the non-useful contaminants. To do this a variety of flotation reagents may be used in a succession of steps each to perform its particular function on some particular contaminant. In such a case, the reagents obviously can not be added to the recovery system effectively at any other point than just prior to the flotation stage in which the particular reagent is necessary. Except in these cases, however, the present invention is not limited to any particular point at which the flotation reagents are to be introduced into the circuit.

' It is apparent, therefore, that an important advantage of the present invention is that its scope is very broad. Neither the apparatus nor the process of the present invention .is necessarily limited to any particular type of lubricating coolant, or to the vclarification of coolants which have been used while processing lworkpieces of a particular class of materials or to any particular type of material-modifying operation.

The invention will be described in greater detail in conjunction with the following specific examples which are meant to be merely illustrative and do not in any way limit the invention. All parts are by weight unless otherwise noted.

WATER OR AQUEOUS SOLUTIONS AS COOLANTS Example 1 In the fabrication of hard rubber articles by procedures involving grinding and cutting operal0 a cumbersome apparatus, the screen requires frequent cleaning.

A sample of unscreened water was found to contain about 1.03 parts/1000 of solids. A sample of the unscreened water was given a 30 second flotation in a Fagergren flotation machine using 0.5 lb./ton of black liquor soap as a flotation promoter. 0.99 part of solids/1000 parts of feed were recovered. The use of the flotation cell, therefore, will eliminate the necessity for the screening apparatus and at the same time provide a rapid and continuous procedure for recovering the solids. Repeated tests with other anionic reagents gave equally satisfactory recovery.

Example 2 Water used as a coolant in grinding molded pieces of a urea-formaldehyde type resin was floated for 2 minutes in a Fagergren flotation machine using 0.5 lb./ton of black liquor soap. This 2minute flotation treatment recovered 95% of the suspended solids.

Example 3 A 2000 cc. sample of water which had been used as a coolant in grinding a Bakelite molding was aerated strongly for l minute using l lb./ton of kerosene and 1 lb./ton of black liquor soap. Vacuum was then applied to the surface of the suspension. A floating layer separated out and was drawn 01T. Approximately 86% of the solids were recovered in this manner.

Example 4 A 2000 cc. sample of water containing 3.82 gms. of 100 mesh glass particles picked up in a grinding operation was floated for 45 seconds in a laboratory size Fagergren flotation machine using 1 1b./ton of laurylamine hydrochloride as a reagent. Substantially of the glass particles was removed.

Eample 5 2000 cc. samples of contaminated coolants originally comprising 0.5 lb./gal. of sodium carbonate contaminated with iron and steel particles were floated for 2 minutes in a laboratory size Fagergren flotation machine using 0.043 lb./ton of dicresyl dithiophosphate as a reagent. The average feed contained 3.16 parts/1000 of suspended solids of which 2.68 parts/1000 parts of feed were removed by the flotation process.

In the manufacture of copper wire, tubing,

r sheets and the like, water or aqueous solutions of saponified fatty acids, crude fats, etc. are frequently sprayed on the dies, rolls, bearings and workpieces both as lubricants and coolants. This fluid picks up considerable quantities of copper particles, copper oxide, copper hydroxide and copper salts. Conventional practice involves settling these coolants in large tanks and recirculating the settled coolant. This presents considerable difficulty not only because the material settles very slowly but because the large volumes of coolant required necessitate extremely large storage capacities. In addition, the attempted clarification by settling is seldom complete and as a result hard particles are often recirculated. This produces excessive wear on the bearings, dies and rolls and necessitates frequent shutdowns for repair, adjustment or frequent replacement. Further the copper or copper compounds have an intrinsic value if they can be recovered in suitable form.

Example 6 A sample of water used in a copper rolling operation was found to contain 0.615 part of suspended solids per 1000. Samples of this water were treated for varying intervals in a flotation machine using 0.3 lb./ton of black liquor soap. It was found that flotation treatments of 1/2 minute or more readily reduced the solids content of 'the ellluent to as low as about 0.007 part per 1000.

Example 7 Samples of a contaminated wire dip originally prepared from water and a saponied fat were found to contain metallic copper particles and a sludge of copper hydroxide and various copper soaps. Samples were subjected to treatment for 2 minutes in a Fagergren flotation machine. No reagents were required. Samples fed to the machine averaged 9.5 parts/ 1000 of solids and a very eiective clarification was made. Filtrations on the clarified effluent showed that complete removal of solids was obtained by the flotation treatment.

Example 8 A sample of spray water used for washing copper Wire after a pickling operation and containing 0.084 part of metallic copper per 1000 was treated in a Fagergren flotation machine for 1 minute in the presence of 0.5 lb. of black liquor soap per ton of liquid. The eilluent from the ilotation treatment contained 0.002 part of suspended solids per 1000 parts of liquids.

Example 9 Water used as a coolant in grinding operations on iron and steel became so badly contaminated with metal particles and abrasive grit that the circulating pump had to be replaced at frequent intervals. This suspension containing about 0.25 1b. of sludge per gallon of liquid, was passed through a flotation machine. With 0.5 lb./ton of black liquor soap as a reagent, practically complete removal of solids was obtained. Kerosene in combination with black liquor soap gave high clarity. Talloel, saponied or in the form of an emulsion, also produced high clarity when used as a flotation reagent.

It is therefore apparent that the use of a flotation machine obviates the necessity for the large settling basins which have been previously used, provides a rapid and continuous method of clarification and recovers the copper-bearing or other metallic material in a suitable form for reclaiming. It was also found that it was unnecessary to treat the entire flow of cooling water by flotation in order to effectively prolong the active life of the rolls and dies. A continuous flotation process withdrawing from about 15 to 50% of the flow and clarifying it before reuse was found to be effective in cutting down the previously necessary idle periods during which. the rolls, dies, and bearings were being repaired or replaced. In those processes in which drawn or extruded materials are passed directly into a washing and cooling dip the same system may be used to recover waste products and clarify the coolant.

OIL AS A COOLANT Example 10 Lubricating oils which had been used as coolants in machining operations on magnesium alloys were found to possess no collecting power when treated in a Fagergren flotation machine with or without additional flotation reagents.

Example 1 1 Carbon tetrachloride used as a dip bath in degreasing samples which had been milled using oils as a lubricating coolant was found to be contaminated with oils, grease and metallic particles. Samples were diluted with water and subjected to the procedure of Example 10. No froth overflow occurred but substantially all the contaminants collected at the interface when the emulsion separated. The decanted carbon tetrachloride was reused. Because of the high volatility of the carbon tetrachloride it was found necessary to enclose the flotation cell.

SOLUBLE-OIL TYPE EMULSIONS AS COOLANTS Example 12 2000 parts of used, contaminated emulsion containing sludge, metal particles and abrasive grit were subjected to flotation without the use of any additional reagents for 2 minutes using a rotor speed of 1500 R. P. M. rPhe solids floated readily and the froth gradually increased in volume as the solids were removed. Analysis of the clarified liquors indicated that 99.98% of the contaminants had been removed by this flotation treatment.

Several such portions were treated in this manner. In every case the operation left a substantially completely clarified emulsion. The froth concentrate in each case was allowed to stand and the solids separated readily therefrom by settling. The supernatant liquid was decanted and added to the flotation feed in a subsequent portion of contaminated emulsion. In each case practically complete removal of the suspended solids was obtained and the clarified emulsion was found suitable for use.

Example 13 The procedure of Example 12 was tried on a sample of another used emulsion and only 91.53% of the solids was found to be removed. The experiment was repeated using an alcoholic solution of ammoniated talloel in an amount equal to 0.1 lb./ton of emulsion as a promoter. The sample was conditioned for 15 seconds with the reagent and then floated for 11/2 minutes. The use of the reagent appeared to speed up flotation. Analysis of the clarified emulsion indicated that 99.96% of the contaminants had been removed.

As has been pointed out most of the contami nated coolants found in actual practice contain a certain amount of material which may be more or less readily settled. Advantage can be taken of this fact to relieve the load imposed upon the flotation process and thereby in many cases escape the use of excessive amounts of reagent. This procedure will be illustrated by the following example.

Example 14 A 2000 cc. sample of a'contaminated emulsion was found to have a variety of contaminants, a portion of which floated readily, a portion tending to remain suspended and a portion which tended to settle. The sample was allowed to stand for a period of minutes at the end of which time a considerable portion of the contaminants were found to have settled. This portion contained most of the coarser particles of metal and made up about 15% of the total impurities. The supernatant liquid was then decanted and subjected to froth flotation as in Example 12. no added reagents being required. Examination of the clarified emulsion indicated that it was substantially free from all impurities.

A substantially 100% clarification of the emulsion was readily produced by this combination of settling and flotation. This is of particular advantage in those cases where the coarser material requires either an expensive reagent for successful flotation or excessive amounts of reagents.

Where the nature of the emulsion permits, settling aids may be used to increase the proportion of the material removed before the flotation step. A number of well-known wetting agents were tried as settling aids. It was found, curiously enough, that the same compounds which were most effective as cationic-type flotation promoters were most effective in settling the solids. The following agents and proportions appeared to be most effective in clarifying the contaminated emulsion of Example 14: the reaction products of poly-ethylene poly-amines and mixed fatty acids or about C12 in the ratio of 2.5 lbs/ton; n-decyl and n-tetra-decyl pyridinium chloride in amounts of about 3 lbs/ton and Lorol amine hydrochloride in a ratio of about 5 lbs/ton. While these reagents were most effective with this sample, the invention is not meant to be so limited.

Some reagents such, for example, as the mixed poly-ethylene poly-amine reaction products and Lorol amine hydrochloride are soluble in the original light oil. These reagents therefore possess an added advantage that in many cases they may be added to' or compoundedwith the original light oil solution and allowed to remain present throughout future operations, thus being ready at all times to perform their intended function.

In many cases where the lubricating function is of equal or greater importance than the cooling function, it becomes desirable to introduce a water-immiscible lubricating oil into the coolant. Because of their immiscible nature as contrasted with the so-called water-soluble oils these lubricating oils readily separate into a supernatant layer if the coolant is allowed to stand. Often a major portion of the contaminants will remain in this non-soluble oil layer. The layers may be separated, as by decantation, the oil layer puriiledas in Example and the residual llayer treated as in Example 1 or Examples 12-14 depending upon its nature and the nature of the contaminants.

Example A soluble-oil" type emulsion containing 1 part of original oil to about 4 parts of water was used for cooling and lubricating purposes on a multiple drill press operating on magnesium metal- During the drilling operation the coolant became contaminated with metal particles. dirt and decomposition sludge. The machine was equipped with a conventional settling tank for clarifying the coolant. This tank was found to be not only ineffective in providing a useful clarification but became so quickly clogged with such material as did settle as to require frequent stoppages of the machine to clean out settled matter from the tank. Instead of using the conventional settling tank the entire coolant flow was passed through a string of two 12 Fagergren flotation machines at a flow rate of about 3 gals/min. without the use of any additional reagents. Substantially of the suspended metal and grit particles were found to be removed and at the same time a large amount of the breakdown sludge was also` removed.

Example 16 A soluble-oil type emulsion prepared by diluting 1 -part of original oil with 40-50 parts of water was used as a lubricating coolant in grinding operations on a variety of metals. The grinding machinery in each case was equipped with the conventional, baflled settling-tanks intended to clarify the coolant. The used emulsion was passed to these tanks which removed the larger particles and agglomerates of solid matter andthe emulsion was then passed through a string of two 12 Fagergren flotation machines without the use of additional flotation reagents. The results obtained in continuous operation over periods of several days are shown in the following table:

Metal Treat-ed I Per Cent Removal of Solids steel 99.8. Cast Iron .L Complete. Mixture of Cast Iron and Bronze! Bronze In addition to the very complete removal of the metal particles and grit, as indicated above,

Eample 17 The procedure'of Example 16 was repeated using a single 12" Fagergren flotation machine and a flow rate of from 2 to 4 gals/min. The entire flow of emulsion was passed directly to the flotation machine without rst being passed through the settling tanks. In each case a removal of more than 99% of the solids was obtained.

This clearly demonstrated that the use of the settling tanks was unnecessary and that they could be readily replaced by flotation cells which required less space for operation, were much more certain and dependable in operation, and did not require frequent shut downs to remove the settled particles from the tanks.

Example 18 A sample of a soluble-oil emulsion containing about l part of original oil to 40 parts'of l. Before the settling tank 2. Between the'settling tank and centrifuge 3. After the centrifuge.

At point 1 the removal of solids was about 99% complete. At point 2 the flotation feed was found to contain a substantial amount of finely divided particles which were substantially completely removed. At point 3 the flotation feed was found to contain some extremely fine suspended solids of which a substantial proportion was removed by the flotation machine.

As pointed out in our previously-mentioned copending application the use of a flotation machine was found to be particularly advantageous in the case of extremely finely divided particles. A microscopical examination of the several contaminated emulsions as fed to the flotation cell indicated that much of the impurity existed in the form of very ne particles which exhibited Brownian movement and were apparently free. An examination of a sample of the clarified emulsion indicated that substantially all material having a particle size larger than 1 micron had been removed. In addition, examination of a representative portion of the concentrate indicated that considerable amounts of material having a particle size less than 1 micron had been removed as well as those of larger size. The majority of these fine particles present in the concentrate were in the form of agglomerates. Apparently the action of the flotation cell is not only to remove all the particles above a certain size but also to cause agglomeration of those of smaller size which results in their subsequent removal.

Example 19 Since settling has been considered in the pasti, to be a pra-ctical method of clarifying contaminated coolants, with the exception of extremely large installations in which filters and centrifuges could be used in conjunction therewith, emulsion type coolants are frequently prepared VVin such a way that solid matter settles more readily therefrom. This type of lubricating coolant is most frequently used in precision grinding operations where exact dimensions'must be obtained. However, even such coolants pick up suspended solids as contaminants which can not be removed in any reasonable time of settling. The presence of these contaminants is particularly objectionable in the precise type of work for which the coolants are specifically intended.

A sample of such a precision grinding coolant which had been used in operations on bronze and steel was found to contain 0.602 part per 1000 of finely divided solids. After a 30 second flotation in a Fagergren flotation machine, without reagents, the solid content was reduced to about 0.001 part/ 1000 indicating a removal of about 99.8%.

The flotation process may be in some cases advantageously used in combination with other known separation processes such as tabling, filtering, centrifuging and the like. This combination of processes is especially advantageous in those cases where the contaminated emulsion con- 16 tains solid particles of greatly varying particle size. By applying one of these methods to the emulsion as a whole, portions which are difficult to float and yet can not readily be removed by settling may be separated and thereby reduce the work which must be done by the flotation. In certain cases it may also enable very appreciable savings in the amount of reagents required. The following example illustrates a process in which flotation and tabling processes may be combined.

Example 20 Several gallons of used emulsion containing sludge, grit and metal particles of varying size were treated on a laboratory Wilfley table. Solids, relatively coarse in particle size and amounting to about 35% of the total solids. were removed by this treatment. The residual liquid was then subjected to the procedure of Example l2. A substantially completely clarified emulsion was produced.

A combination of two processes such as the flotation and tabling of Example 20 greatly adds to the efficiency and flexibility of the overall procedure of the present invention.

An obvious modification is to first treat the whole emulsion by a flotation step in order to remove the fines and then table the residual emulsion in order to remove particles which could not be readily floated. While a good clarification can be produced in this way, it has the disadvantage of having the large pieces present during the flotation step where they can do no good and may cause trouble.

As was also pointed out in the above discussion, in many cases the recovery of one or more of the contaminants may be equally important with the reviviflcation of the coolant. The procedure in such a case will be illustrated by the following example.

Example 21 A 2000 cc. sample of a sludge-containing emulsion which had been used in the processing of aluminum parts was treated as in Example 12 above. Approximately 20 cc. of liquid were removed with the froth concentrate and approximately 1980 cc. remained in the flotation cell. The solids were removed from the froth concentrate and divided into 3 approximately equal portions each being treated respectively with benzene. carbon tetrachloride and acetone to remove oil and grease. 'Ihe metal particles settled out from the solvent in a substantially oil-free condition and the oil-containing solvent was removed by decantation. In each case the metal particles were separated in a form suitable for recovery. Satisfactory results were obtained in each case. However, the metal particles settled more freely from the acetone solutions and therefore this solvent appears to possess a certain advantage.

Substantially of the aluminum was re- Y moved from the contaminated emulsion by the flotation treatment. Essentially, a complete recovery of aluminum was therefore obtained. It is therefore apparent that the flotation treatment has an extraordinarily high efliciency, whether from the point of view of recovering fine metal particles of this type or from the point of view of clarifying the coolant.

While only benzene, carbon tetrachloride and acetone were mentioned in this example the process is by no means so limited. The choice of the solvent would depend upon the particular oils, greases or other contaminants which were to be removed from the metal. In some cases a plurality of solvents in succession may be required to accomplish an adequate extraction. A simple distillation serves to`recover the solvent and thereby permits it to be reused.

With contaminated coolants from many metalworking shops the bulk of the contaminants will comprise particles of magnetizable material such as iron or steel. It is possible to take advantage of this property in a number of different ways. For example, the magnetizable material may be made to settle from the coolant by the use of a magnetic field. A sample containing magnetizable material was settled by the aid of a magnetic field. This produced 99.'7 to 99.9% removal of all the suspended solids in some cases butin others it was found that an effective clarification could not be made in this manner. Samples of this latter type were then subjected to flotation as in Examples 12 and 13. A magnetic field was then found to be effective in pulling the magnetizable material from the froth concentrate.

By first subjecting the used coolant to a flotation step and then flowing the froth concentrate across a magnetic separator the magnetizable material can be recovered per se. Alternatively, the whole coolant before the flotation step may be flowed across a magnetic separator and the flotation step then applied. This procedure, while giving good clariflcation, did not give quite as good a separation of cleaned magnetizable material as did the magnetic treatment of the froth concentrate after flotation.

The combination of magnetic separation and flotation in which the coolant is first passed over a magnetic separator and then floated is especially advantageous however in the case where the contaminants comprise both magnetizable material, such as iron or steel,A and non-magnetizable particulate material such as aluminum or brass. This procedure will be illustrated by the following example.

Example 22 A 2000 cc. sample of used emulsion containing about 5% of soluble oil, about 0.99 part/1000 of finely divided iron filings and about 1.80 parts/ 1000 of finely divided aluminum metal was caused to flow through a magnetic field. The

emulsion after passing the magnetic separator was transferred to a flotation cell and treated as in Example 12. The residual emulsion after flotation was found to be 99.98% free from suspended solids. The iron and aluminum contained in the froth concentrate were readily separated by drying and magnetic treatment. Examination of the material removed by the first magnetic treatment proved it to comprise approximately 95% of the iron and a portion of aluminum. The aluminum was readily recovered by drying the mass and removing the steel from it by a further magnetic treatment.'

With some samples of contaminated coolant it will be found that on application of the magnetic eld the non-magnetizable metallic contaminants will beV pulled down with the magnetizable material. This may be caused by a number of external factors such as mechanical agglomerization, the binding action of certain oils and the like. In such cases the procedure set forth in Example 22 may be modified by dispersing the precipitated metallic mixture in a suitable fluid and then reapplying the magnetic field. This is illustrated by the following example.

, Example 23 A sample of the same contaminated coolant of Example 19 containing grit, steel and bronze particles was subjected to the procedure of Example 21. The first magnetic treatment removed all the metallic contaminants except those of very fine size as a sponge-like mass. This mass was removed from the magnetic separator, dispersed in an acetone-water solvent and again flowed across the magnetic separator. vThe steel particles were precipitated substantially free from bronze. The bronze was recovered by filtering and drying and appeared to contain very few steel particles.

ExampleI 24 Example 25 A wire dip prepared from a soap, tallow and a vegetable oil and used for the same purpose as that described in Example '7 and contaminated with essentially the same type of materials was readily clarified by flotation without the use of additional reagents. From a feed to the flotation machine, containing 2.62 parts of suspended solids per 1000 parts of dip, over 99% of the solids were removed in a 1.5-minute flotation treatment.

Example 26 A contaminated coolant similar to that described in the grinding operation on bronze in Example 16 was also used in a steel grinding operation. This coolant was treated with a commercial disinfectant containing formaldehyde.

, 1 part of disinfectant to 400 parts of coolant was used.

Before treatment 99.5% of the contaminating solids were removed by notation treatment. The

yflotation operation was stopped to allow the disinfectant to mix thoroughly with the coolant. The flotation treatment was then continued and. 99.6% of the suspended solids was removed, indicating that the addition of the disinfectant had no appreciable effect on the flotation clarification process.

It will be apparent, therefore, that the operating circuit and procedure of the present invention incorporates a number of important advantages over any previously-used procedures. This is true whether the invention is considered from the point of view of an improved material-modifying operation or whether it is considered solely from the point of view of clarifying n`tli`e\coolant. and recovering the contaminants therefrom.

We claim:

1. A continuously-operating, self-cleaning, ma\\u terial-modifying circuit comprising the combination of a material-modifying means, adapted to physically modify a solid material in the presence of a liquid coolant whereby in the normal operation of said means said coolant becomes contaminated, with a coolant-clarifying circuit,

adapted to remove said contaminants from said coolant; the combination being characterized in that said coolant-clarifying circuit combines a treating vessel adapted to hold a substantial body of coolant; conduit means adapted to introduce used coolant into said vessel; agitating and aerating means positioned within said vessel, adapted to produce a multiplicity of small bubbles in the coolant in said vessel, the normal rise of said bubbles through said coolant resulting in concentration of a major portion of the contaminants in an upper layer in said vessel; means adapted to remove said contaminant-bearing upper layer from said vessel; means adapted to remove treated coolant from said Vessel and conduit means adapted to return removed coolant to said material-modifying means.

2. A material-modifying circuit according to claim 1, in which the agitating and aerating means comprises the rotor and stator of a mechanical-type flotation unit.

3. A material-modifying circuit according to claim 1, including in addition a storage vessel for treated coolant; conduit means adapted to conduct treated coolant from the treating vessel to said storage vessel and from said storage means to said material-modifying means.

4. A material-modifying circuit according to claim 1, including in addition a storage vessel adapted to hold a second body of coolant and means adapted to transfer treated coolant from said treating vessel to said storage vessel; characterized in that the material-modifying means is so positioned that modified material is contacted with said second body of coolant in said storage vessel.

5. A continuously-operating, self-cleaning, material-modifying circuit comprising the combination of a material-modifying means, adapted to physically modify a solid material in the presence of a liquid coolant whereby in the normal operation of said means said coolant becomes contaminated, with a coolant-clarifying circuit, adapted to remove said contaminants from said coolant; the combination being characterized in that said coolant-clarifying circuit combines a treating vessel adapted to hold a substantial body of coolant; conduit means adapted to introduce used coolant into said vessel; agitating and aerating means positioned within said vessel adapted to produce a multiplicity of small bubbles in the coolant in said vessel, the normal rise of said bubbles through said coolant resulting in concentration of a major portion of the contaminants in an upper layer in said vessel; means adapted to remove said contaminant-bearing upper layer from said vessel; a storage vessel adapted to hold a second substantial body of said coolant; means adapted to remove treated coolant from the treating vessel and into said storage means; and conduit means adapted to conduct coolant from said storage means to said material-modifying means.

6. A material-modifying circuit according to claim including in addition means adapted to introduce an additional liquid into said treating vessel, said liquid being disseminated in said coolant by the normal operation of said agitating and aerating means; a separating vessel; conduit means adapted to convey said disseminated liquid-coolant mixture from said treating vessel to said separating vessel; and conduit means adapted to convey separated coolant from said separating means to said storage means.

7. The method of continuously clarifying and restoring to condition for continued reuse a used lubricating coolant, consisting of a water-insoluble, water-immiscible oil material contaminated with metallic and non-metallic solid particles and exhibiting substantially no tendency to form a supernatant froth layer containing said solid contaminants when subjected to aeration and agitation; which method comprises the steps of admixing said used coolant with water; establishing a xed volume of the resultant coolant-water mixture; continuously and simultaneously subjecting said body of mixture to aeration and intense agitation, whereby a supernatant froth layer is formed on said body and substantially all the solid contaminants rise through said body and are concentrated in said froth layer removing contaminant-bearing froth from said froth layer at substantially the rate at which said froth layer is being formed, withdrawing substantially contaminant-free coolant-water mixture from said body, at a level below said supernatant layer; adding to said body, at a level below that at which claried mixture is withdrawn, additional amounts of contaminated coolant and water; maintaining the rates of removal of clarified coolant-water mixture and addition of water and contaminated coolant substantially constant and such that the average period of dwell of fluid in said body is sufficient to allow substantially all said solid contaminants to be concentrated in said froth layer and such that the total volume of said 'body of coolant-water mixture plus said contaminant-bearing froth layer remains substantially constant; separating said removed claried coolant-water mixture into separate oil and water layers and collecting the separated oil layer.

ROBERT BEN BOOTH. NORMAN MORASH.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 835,120 Sulman et a1 Nov. 6, 1906 1,310,051 Blomiield July 15, 1919 1,388,868 Jones Aug. 30, 1921 1,455,187 Brown May 15, 1923 1,505,944 Broadbridge et al. Aug. 26, 1924 1,693,885 Butterworth Dec. 4, 1928 1,876,243 Kelly Sept. 6, 1932 1,892,950 Houpt Jan. 3, 1933 1,963,122 Fagergren June 19, 1934 2,065,053 Christmann Dec. 22, 1936 2,101,331 Fagergren Dec. 7, 1937 2,140,289 Hurtt et a1 Dec. 13, 1936 2,153,449 Booth Apr. 4, 1939 2,191,962 Jones Feb. 27, 1940 2,220,574 Little et al Nov. 5, 1940 2,252,385 Orozco Aug. 12, 1941 2,274,658 Booth Mar. 3, 1942 2,335,209 Booth Nov. 23, 1943 2,347,147 Booth Apr. 18, 1944 2,352,365 Booth June 27, 1944 

1. A CONTINUOUSLY-OPERATING, SELF-CLEANING, MATERIAL-MODIFYING CIRCUIT COMPRISING THE COMBINATION OF A MATERIAL-MODIFYING MEANS, ADAPTED TO PHYSICALLY MODIFY A SOLID MATERIAL IN THE PRESENCE OF A LIQUID COOLANT WHEREBY IN THE NORMAL OPERATION OF SAID MEANS SAID COOLANT BECOMES CONTAMINATED, WITH A COOLANT-CLARIFYING CIRCUIT, ADAPTED TO REMOVE SAID CONTAMINANTS FROM SAID COOLANT; THE COMBINATION BEING CHARACTERIZED IN THAT SAID COOLANT-CLARIFYING CIRCUIT COMBINES A TREATING VESSEL ADAPTED TO HOLD A SUBSTANTIAL BODY OF COOLANT; CONDUIT MEANS ADAPTED TO INTRODUCE USED COOLANT INTO SAID VESSEL; AGITATING AND AERATING MEANS POSITIONED WITHIN SAID VESSEL, ADAPTED TO PRODUCE A MULTIPLICITY OF SMALL BUBBLES IN THE COOLANT IN SAID VESSEL, THE NORMAL RISE OF SAID BUBBLES THROUGH SAID COOLANT RESULTING IN CONCENTRATION OF A MAJOR PROTION OF THE CONTAMINANTS IN AN UPPER LAYER IN SAID VESSEL; MEANS ADAPTED TO REMOVE SAID CONTAMINANT-BEARING UPPER LAYER FROM SAID VESSEL; MEANS ADAPTED TO REMOVE TREATED COOLANT FROM SAID VESSEL AND CONDUIT MEANS ADAPTED TO RETURN REMOVED COOLANT TO SAID MATERIAL-MODIFYING MEANS.
 7. THE METHOD OF CONTINUOUSLY CLARIFYING AND RESTORING TO CONDITIN FOR CONTINUED REUSE A USED LUBRICATING COOLANT, CONSISTING OF A WATER-INSOLUBLE, WATER-IMMISCIBLE OIL MATERIAL CONTAIMINATED WITH METALLIC AND NON-METALLIC SOLID PARTICLES AND EXHIBITING SUBSTANTIALLY NO TENDENCY TO FORM A SUPERNATANT FROTH LAYER CONTAINING SAID SOLID CONTAMINANTS WHEN SUBJECTING TO AERATION AND AGITATION; WHICH METHOD COMPRISES THE STEPS OF ADMIXING SAID USED COOLANT WITH WATER; ESTABLISHING A FIXED VOLUME OF THE RESULTANT COOLANT-WATER MIXTURE; CONTINUOUSLY AND SIMULTANEOUSLY SUBJECTING SAID BODY OF MIXTURE TO AERATION AND INTENSE AGITATION, WHEREBY A SUPERNATANT FROTH LAYER IS FORMED ON SAID BODY AND SUBSTANTIALLY AL THE SOLID CONTAMINANTS RISE THROUGH SAID BODY AND ARE CONCENTRATED IN SAID FROTH LAYER REMOVING CONTAMINANT-BEARING FROTH FROM SAID FROTH LAYER AT SUBSTANTIALLY THE RATE AT WHICH SAID FROTH LAYER IS BEING FORMED, WITHDRAWING SUBSTANTIALLY CONTAMINANT-FREE COOLANT-WATER MIXTURE FROM SAID BODY, AT A LEVEL BELOW SAID SUPERNATANT LAYER; ADDING TO SAID BODY, AT A LEVEL BELOW THAT AT WHICH CLARIFIED MIXTURE IS WITHDRAWN, ADDITIONAL AMOUNTS OF CONTAMINATED COOLANT AND WATER; MAINTAINING THE RATES OF REMOVAL OF CLARIFIED COOLANT-WATER MIXTURE AND ADDING OF WATER AND CONTAMINATED COOLANT SUBSTANTIALLY CONSTANT AND SUCH THAT THE AVERAGE PERIOD OF DWELL OF FLUID IN SAID BODY IS SUFFICIENT TO ALLOW SUBSTANTIALLY ALL SAID SOLID CONTAIMINANTS TOI BE CONCENTRATED IN SAID FROTH LAYER AND SUCH THAT THE TOTAL VOLUME OF SAID BODY OF COOLANT-WATER MIXTURE PLUS SAID CONTAMINANT-BEARING FROTH LAYER REMAINS SUBSTANTIALLY CONSTANT; SEPATATING SAID REMOVED CLARIFIED COOLANT-WATER MIXTURE INTO SEPARATE OIL AND WATER LAYERS AND COLLECTING THE SEPARATED OIL LAYER. 